The search service, at APIs.io, will leverage the open source APIs.json metadata format, which provides a common discovery mechanism for API providers to publish information about APIs.

"APIs.io is a search engine, and what is discovers is machine-readable descriptions of APIs," said Steven Willmott, CEO of 3scale, which provides API infrastructure.

3scale hopes its site becomes a Google for APIs. "I think it's a bit of a stretch right now, given [adoption is] very small but that's the objective," Willmott said.

APIs.io would not be the first API search engine. ProgrammableWeb, an informational site about Web APIs, already has one, but it requires manual entry by API publishers. A hosted format like APIs.json, though, could suffer spam issues, said ProgrammableWeb Editor-in-Chief David Berlind. "To give you an idea, we get thousands of bogus submissions per day. We can see that machines have been built to defeat things like Captcha in hopes of populating our directory with listings that point to all sorts of crazy stuff." ProgrammableWeb has put in place processes and infrastructure to ensure quality of its directory, Berlind said. Also, ProgrammableWeb will enter API data on behalf of interested publishers who would rather defer on this responsibility.

A representative of APIs.io said it was unlikely the search engine would sustain spam problems. A FAQ on APIs.io said directories like ProgrammableWeb "do a great job of curating APIs, but this is a hard challenge to maintain as the number of APIs grows rapidly. We hope that by encouraging people to update and maintain information on their API on their own domain it will be possible to scale API discovery much more easily."

API builders populate APIs.io by generating an APIs.json file using a generator tool provided on the APIs.io site. APIs.io will crawl known APIs.json files and top domains on Alexa. There are about 50 APIs in the search engine now and plans call for attracting many more. "The number of APIs [at large] is going up so fast, we need an automated way to keep track of them," Willmott said. He estimated there are 10,000 to 20,000 APIs available now.